Radio Horizon and Line-of-Sight Distance Calculator
How far can two towers see each other?
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Radio Horizon and Line-of-Sight Distance Calculator by TheCalcTools
How the Radio Horizon and Line-of-Sight Distance Calculator works
Enter the heights of both antennas above flat ground or sea.
Each antenna’s horizon is 3.572 √(k h) kilometres with h in metres.
The line-of-sight distance between them is the sum of the two horizons.
The formula
Worked example
Using the default values shown in the calculator:
| Antenna 1 height (m) | 45 |
|---|---|
| Antenna 2 height (m) | 30 |
| Effective earth radius factor k | 1.33 |
- Antenna 1: 3.572 √(1.33 × 45) = 27.6 km; antenna 2: 22.6 km.
- Maximum line-of-sight distance = 50.2 km.
Result:
| Horizon of antenna 1 (km) | 27.6 |
|---|---|
| Horizon of antenna 2 (km) | 22.6 |
| Maximum LOS distance (km) | 50.2 |
Frequently asked questions
Why does k = 4/3 give 4.12√h?
3.572 × √1.33 ≈ 4.12, the familiar radio-horizon formula, which is longer than the optical horizon because the atmosphere bends radio waves.
Does terrain matter?
Yes. This is the limit over smooth earth. Hills and buildings shorten it; use the Fresnel/LOS calculator for a specific path.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.